Humans can function optimally, in comfort, over only a fairly narrow ambient temperature range. Adjustment of the amount and type of clothing will afford some relief from ambient temperature, especially adding clothing for comfort in a cold environment. However, as temperature rises conditioning the ambient air, typically by some form of heat extraction often, is the only solution to maintaining a comfortable, tolerable air temperature. Typically, such heat extraction is performed by air conditioners. Air conditioners operate on the principle of heat absorption as a composition such as freon or other refrigerant changes phase from a liquid to a gas. Water, for example, will absorb about 550 calories of heat per gram when changing from water at 100° C. to water vapor at 100° C. (at one atmosphere of pressure). On the other hand, one gram of water will release 540 calories of heat when changing from water vapor at 100° C. to liquid water at 100° C. Air conditioners, however, are heavy, expensive and complex. Also, they require compressors to provide energy to power the gas to liquid phase change. Furthermore, they are designed to condition air masses defined by buildings or vehicle structures such as a room of a building or an interior compartment of a vehicle, rather than conditioning the air directly adjacent to the body of an occupant, that is, the occupant's “microenvironment”.
Air conditioners are undesirable, for example, in cooling a cabin of a small or light aircraft such as a 2, 4 or 6 place airplane. In such light aircraft, there is a fairly small cabin space and anything that adds weight to the aircraft decreases its performance and payload. Thus, many light aircraft do not have air conditioning systems. Moreover, complicating this deficiency is the often limited ability to move air between the outside and the inside of the aircraft via ducts or windows. Thus, it may often get quite warm in the small interior cabin space of a light aircraft, especially when it is parked or tied down for a period of time on an airport apron. The warm air cabin environment of a light aircraft is not conducive to the concentration required for the pilot to operate the aircraft, especially during critical take-off or landing procedures. After the aircraft climbs to altitude, the outside air is usually sufficient to cool, even with small ducts, the interior of the aircraft cabin. However, this does not help when the aircraft has been sitting for a period of time in the hot air on the ground.